Conventionally, as a connector for electrically connecting a circuit board such as a touch panel and an electronic part, a flexible printed circuit (hereinafter, called an “FPC”) is used. The FPC is thermal-compression-bonded to a circuit board via an anisotropic conductive film (hereinafter, called an “ACF”). The circuit board and the FPC are aligned using alignment marks provided near connection regions so that they are not bonded in a state where connection terminals in the circuit board and connection terminals in the FPC are deviated from each other.
The alignment mark in the FPC is formed by copper foil which is the same as a wire in the FPC. Since copper is a metal having low light transmittance (hereinafter, called an “opaque metal”), visibility of the alignment mark formed by copper foil is high.
On the other hand, the alignment mark for the circuit board is often provided together with the connection terminal in a region from which a protective film on the board is removed. When the connection terminal is formed by an opaque metal film, the connection terminal absorbs moisture in air and becomes susceptible to corrosion. When the connection terminal is formed by a stacked film made of an indium tin oxide (hereinafter, called “ITO”) film and an opaque metal film, the ITO film easily peels off in the interface with the opaque metal film. Thus, in the case where the connection terminal in the circuit board includes the opaque metal film, there is a problem such that reliability of the connection part between the FPC and the circuit board is not assured. When the connection terminal in the circuit board is formed only by the ITO film, the problem is solved. Further, when the alignment mark is also formed by the ITO film, positional deviation between the alignment mark and the connection terminal does not occur, so that alignment in the circuit board and the FPC can be performed with higher precision.
Japanese Patent Application Laid-Open No. Hei 7-128675 discloses a method of manufacturing a liquid crystal display device in which a transparent electrode in a display unit is less visible and a transparent electrode in a terminal part and an alignment mark are visible. The electrodes and the mark are formed by an ITO film on an insulating substrate. A soluble organic thin film is formed on the transparent electrode in the terminal part and on the alignment mark and, after that, the insulating substrate is thermally treated. Since oxidation in the transparent electrode in the display unit proceeds by thermal treatment, the transmittance of the transparent electrode in the display unit becomes higher as compared with that prior to the thermal treatment. However, the transparent electrode in the terminal part and the alignment mark are covered with the organic thin film, they are not oxidized by the thermal treatment. In such a manner, while maintaining the display quality of the display unit, the transparent electrode in the terminal part and the alignment mark are made visible.    [Patent Document 1] Japanese Patent Application Laid-Open No. Hei 7-128675